Originally Posted by ATPMBA
It may not pick up the trees. I am basing that on an old story that in Vietnam, F111's had ground following radar that would guide the F111 a few hundred feet off the ground in IFR. In some places the jungle growth was 200 feet high or even higher. Needless to say, a few crews did not return.
The ground following radar is forward-looking, not down. A large clearing would tell you to go down, and the 200ft jungle at the other end might get you, if the hillside rising to 1000ft at the other end didn't.
Terrain following is hairy at the best of times.
The consensus here seems to be that the rad-alt will usually latch on to a thick jungle canopy, prefereably wet, but otherwise there may be blips. And non-jungle forests tend to be variable (eh, 411A?) with probably pine forests not showing up at all.
I have also heard of some recent helicopter stories where the RA was not giving back accurate data while flying over water.
Can you elaborate? Unless the surface was glassy calm, I find this difficult to imagine, so, again, I'm interested. (Ancient radar engineer freak here.).